Psicose (D-psicose) is an epimer of the third carbon of fructose (D-fructose), and a functional saccharide which has sweetness like common saccharides but has almost zero calorie since it is not metabolized in the human body, and is thus able to be used as a functional sweetener which can replace sucrose for diabetic and obese patients. In addition, psicose serves to reduce abdominal obesity by controlling enzyme activity involved in lipid synthesis in the liver, and is currently being studied as therapeutic agents for diabetes and arteriosclerosis.
As such, psicose has attracted attention as a sweetener, and in a food industry field, a need for developing a method for efficiently producing psicose gradually arises. Since a small quantity of psicose is present in natural substances during molasses treatment or glucose isomerization, conventional psicose production has been generally carried out through a chemical process. Bilik et al. developed a technique for producing psicose from fructose by utilizing catalysis of molybdic acid ions. McDonald produced psicose in a three-step chemical treatment process from 1,2:4,5-di-o-isopropylidene-beta-D-fructopyranose. In addition, Doner produced psicose by a method of heating fructose with ethanol and triethylamine. However, the psicose production by such a chemical method requires high costs, but has low production efficiency and large quantities of by products.
According to a method for producing psicose by a biological method, Ken Izumori et al. suggested that psicose can be produced from galacitol, D-tagatose or D-talitol by utilizing microbial cell responses. However, these substrates are also relatively rare sucroses or sucrose alcohols present in nature, and thus prime costs thereof are high.
As an enzyme conversion method, there is a method for enzymatically converting fructose into psicose by producing D-tagatose-3-epimerase of a separated microorganism, for example, Pseudomonas cichorii ST-24, in recombinant E. coli and purifying the enzyme, and Ken Izumori et al. has produced psicose at a conversion ratio of approximately 25% using a reaction system for immobilizing D-tagatose-3-epimerase.
According to such a conventional art, to produce psicose from fructose, studies have been conducted to increase psicose productivity by purifying an enzyme and immobilizing the purified enzyme. It is true that the process for purifying an enzyme have needed much time and cost.
Meanwhile, even when piscose is produced, due to similar physical properties to fructose, it is difficult to separate psicose from fructose.
Therefore, there is a demand for a method for producing psicose, which has a high efficiency and can easily isolates psicose.